Cross-reference is made to two U.S. patent applications; Ser. No. 044767, for Added Array Of Molecular Chains For Interfering With Electric Fields, by W. D. Stanbro et al.; and Ser. No. 044761, for Three Dimensional Binding Site Array For Interfering With An Electrical Field, by W. D. Stanbro, which were filed the same date and were assigned to the same entity as this application.
The invention relates to a means for generating an electrical field having a means for interfering with that field. More specifically, the invention relates to an electrode with a porous body having an embedded biochemically active layer.
Electrodes with porous bodies are known. Sintered-anode capacitors in glass-to-tantalum cases are available from the Sprague Co., for instance. Tantalum powder is pressed and heated to produce a sintered porous body. A tantalum wire is embedded as an electrical lead that extends from the body. An amorphous Ta.sub.2 O.sub.5 film is produced electrolytically to electrically insulate and passivate the tantalum. This forms one electrode and a dielectric film of a capacitor which is covered by a glass-to-tantalum case.
In composition analysis, capacitive sensors have been used to determine the concentration of a specific gas in a mixture, or an analyte in a fluid, for example. Such sensors measure a capacitance that changes with the concentration.
Capacitive affinity sensors measure the concentration of an analyte by detecting a change in capacitance as an analyte molecule moves in or out of an electric field between two electrodes of the sensor, for instance. The moving analyte molecule has a low dielectric constant and displaces solvent molecules having higher dielectric constants from a biochemically active layer between the two electrodes. The displacement of the solvent molecules by the analyte molecules reduces capacitance between the two electrodes. The capacitance between the two electrodes is inversely proportional to the concentration of the analyte being measured by such a sensor.
Applicant has developed a capacitor for determining the concentration of an analyte in a fluid, for instance. Biospecific binding reactions occur in a space between electrodes of a capacitive sensor. These reactions occur among molecules of a binding agent immobilized on a surface and an analyte in a fluid. These reactions result in the displacement of small fluid molecules having high dielectric constants by large biochemical molecules having low dielectric constants. This displacement of molecules changes the dielectric constant of the capacitor.
Raymond et al. U.S. Pat. No. 4,571,543 discusses a capacitor for detecting and measuring the concentration of specific nonaqueous materials or constituents in fluids. The capacitor is layered with a coating of silane and then a coating of certain polymers. These polymers form membranes that are permeable to constituents of the fluids. The constituents penetrate through the membrane to change the dielectric constant of a solution under the membrane.
Volgyesi U.S. Pat. No. 4,453,126 concerns a capacitor for monitoring the concentration of anaesthetic gas in a breathing mixture. The capacitor has a dielectric of lipids or elastomers which permit the absorption of the anaesthetic gas to vary electrical characteristics of the sensor.
"Adsorption Of Blood Proteins On Metals Using Capacitance Techniques", by Stoner et al., The Journal of Physical Chemistry, Vol. 74, No. 5, March 5, 1970, describes a differential capacity method for measuring adsorption of proteins on solid metal electrodes.
Arwin et al. U.S. Pat. No. 4,072,576 relates to a capacitive method for studying enzymatic activity and for studying an immunological reaction. An adsorbed polypeptide substrate is used to study enzymatic activity and an antigen is adsorbed onto an electrode surface to study the reaction of the antigen with an antibody.
Molecular Design for Electroanalysis, by Murray et al., Analytical Chemistry, Vol. 59, No. 5, March 1, 1987, discusses chemically modified electrodes for use in sample analysis, and the use of electroactive polymer films, like poly-L-lysine, on such electrodes. These films facilitate oxidation-reduction reactions at the electrodes.
Kinetics of Electron-Transfer Cross-Reactions within Redox Polymers; Coatings of a Protonated Polylysine Copolymer with Incorporated Electroactive Anions, by Anson et al., Journal of the American Chemical Society, Vol. 105, No. 15, 1983, p. 4884, describes electrodes coated with polymer layers that form a three dimensional arrangement of catalytic sites. These layers comprise a random orientation of polymer coils to facilitate oxidationreduction reactions at the electrode. New Model for the Interior of Polyelectrolyte Coatings on Electrode Surfaces; Mechanisms of Charge Transport through Protonated Poly(L-lysine) Films Containing Fe.sup.III (edta).sup.- and Fe.sup.II (edta).sup.2- as Counterions, by Anson et al., Journal of the American Chemical Society, Vol. 105, No. 5, 1983, p. 1096, also describes such electrodes.
In composition analysis, affinity chromatography has been used to determine the presence or concentration of an analyte in a fluid. The analyte is chemically separated or isolated from the fluid, as described in two articles entitled "Affinity Chromatography", one by I. Parikh et al., Aug. 26, 1985, Chemical and Engineering News, pp. 17-32 and the other by R. Walters, September, 1985, Analytical Chemistry, Volume 57, No. 11, pp. 1099A-1114A.
None of the above patents or articles concern a porous electrode having a biochemically active layer embedded in pores of the electrode.